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1、CEMENTEDCARBIDESANDOTHERHARDMATERIALS747CEMENTEDCARBIDESCementedCarbidesandOtherHardMaterialsCarbidesandCarbonitrides.—Thoughhigh-speedsteelretainsitsimportanceforsuchapplicationsasdrillingandbroaching,mostmetalcuttingiscarriedoutwithcarbidetools.Formaterialsthatareverydifficul
2、ttomachine,carbideisnowbeingreplacedbycarboni-trides,ceramics,andsuperhardmaterials.Cemented(orsintered)carbidesandcarboni-trides,knowncollectivelyinmostpartsoftheworldashardmetals,arearangeofveryhard,refractory,wear-resistantalloysmadebypowdermetallurgytechniques.Theminutecarb
3、ideornitrideparticlesare“cemented”byabindermetalthatisliquidatthesinteringtemperature.Compositionsandpropertiesofindividualhardmetalscanbeasdifferentasthoseofbrassandhigh-speedsteel.Allhardmetalsarecermets,combiningceramicparticleswithametallicbinder.Itisunfortunatethat(owingto
4、amistranslation)thetermcermethascometomeaneitherallhardmetalswithatitaniumcarbide(TiC)baseorsimplycementedtitaniumcarbonitrides.Althoughnosingleelementotherthancarbonispresentinallhard-metals,itisnoaccidentthatthegenerictermis“tungstencarbide.”Theearliestsuccessfulgradeswerebas
5、edoncarbon,asarethemajorityofthosemadetoday,aslistedinTable1.Theoutstandingmachiningcapabilitiesofhigh-speedsteelareduetothepresenceofveryhardcarbideparticles,notablytungstencarbide,intheiron-richmatrix.Modernmethodsofmakingcuttingtoolsfrompuretungstencarbidewerebasedonthisknow
6、l-edge.Earlypiecesofcementedcarbideweremuchtoobrittleforindustrialuse,butitwassoonfoundthatmixingtungstencarbidepowderwithupto10percentofmetalssuchasiron,nickel,orcobalt,allowedpressedcompactstobesinteredatabout1500°Ctogiveaproductwithlowporosity,veryhighhardness,andconsiderabl
7、estrength.Thiscombina-tionofpropertiesmadethematerialsideallysuitableforuseastoolsforcuttingmetal.Cementedcarbidesforcuttingtoolswereintroducedcommerciallyin1927,andalthoughthekeydiscoveriesweremadeinGermany,manyofthelaterdevelopmentshavetakenplaceintheUnitedStates,Austria,Swed
8、en,andothercountries.Recentyearshaveseentwo“revolution
